Methods of recovery of oil



june 21, 1956 Filed July 13, 1950 PEOPAN E THEN GAS PQOPANE CoNT/xm me, Ou.

E. v. MUEPHREE ETAL 3,255,933

METHODS E RECOVERY 0E OIL 2 Sheets-Sheet 1 @rn/U19, 7 Clt/Borna.;

une 21, w56 E. v. MURPHREE ETAL 3,256,933

METHODS OF RECOVERY OF OIL Filed July 13, 1950 2 SheeLS-Sheel 2 TDQODUCING GAS UNAIrcEc-I'ED ZoNe I 3 2 I LL ABSQQPTION ZQNE .I LU IL o] 0 y 2 f 9 w DE I H 5 Y IL INITIAL STQIPPIMG u FINAL STRIPPING j v\ ZONE IZESIDUAL ZONE I-I INJECTION WELLS FOQ DQY GAE CONCEMTQATIOM OF Som/ENT IN GAS O @ttor-neg ilnited tates 3,256,933 METHODS F RECVERY 0F OlL Eger V. Murphree and Henry J. Ogorzaly, Summit, N .3., assignors, by mesne assignments, to Esso Production Research Company, Houston, Tex., a corporation of Delaware Filed July 13, 1950, Ser. No. 173,644 Claims. (Cl. 16o-7) tively washes out the crude oil. The driving pressure ofinjected gas is utilized to advance the bank of liquid solvent through the reservoirs and essentially complete recovery of the injected solvent -is o'btained by its vaporization in the recycled gas.

ln conventional crude oil-producing operations, situations are frequently encountered wherein oil wells cease to produce at practical rates, even though it is known with certainty that all available, recoverable oil has not been obtained from the field. This diminution in oil production from a given well may be the result of a number of factors. Generally speaking, in fields not subject to an active water drive, the pressure remaining in the particular oil-producing strata may not be sufcient to cause oil to flow toward and into the well bore hole at a practical and economic rate. Thus, the wells of a -eld tend to become exhausted with respect to primary recovery methods, even when it is known that relatively large quantities of oil are still retained in the reservoirs.

In oil fields characterized .by a significant degree of structural relief, itis common practice to extend the active life of the field by -maintaining its pressure artificially as by injecting gas into the gas ca-p of the reservoir or by injecting water into the porous formation at a level below that of the producing wells. ln addition, it is commonly known to increase the life of a field beyond the normal limit by secondary recovery methods such as Iby Water ilooding, -in which water is continuously injected into the producing sand through injection wells and =displaces a -portion of the residual oil forward into production wells. A similar type of operation may be carried out with gas recycled at low pressure and production increased by this gas drive technique. ln both of these latter procedures, the motion of the oil forward to producing wells after an initial displacement phase results from the fnictional drive of the injected fluids on the residual oil as the injected liiuids move from the injection to the producing Wells. As a result of these relatively ineffective methods of removing oil from the porous sand, substantial quantities of oil remain behind, even after such secondary recovery operations have in turn reached their economic limits.

The gas and Water drives heretofore discussed have generally employed relatively low pressures. More recent proposals for secondary recovery of oil from reservoirs have included the suggestion that gas be recycled at extremely high pressures. Under these conditions, improved recovery of residual oil is obtained because of the increased volume and descreased viscosity of the oil in the reservoir due to solution of components of the gas in the reservoir oil, and due to the increased tendency for vapoarent mice rization of oil in the high pressure gas. The latter phenornenonA is an attribute of operation in the retrograde condensation range in the neighborhood of the critical phase conditions of the reservoir Ihydrocarbon mixture.

Another procedure is to `lill the entire oil reservoir, prefera-bly at increased pressure, with a light hydrocarbon or hydrocarbon mixture or other relatively low viscosity substance soluble in the oil and then to flush out the reservoir with water. In general, it is felt that by this method the injected solute is caused to dissolve in the oil which lessens its viscosity and increases its volume and greatly increases its flowability through the formation. As an alternate to using a single hydrocarbon such as propane alone, the use of natural gas containing light hydrocarbons such as ethane, propane or butanc has also been proposed `for this purpose. ln general, the methods of this type heretofore proposed cause the low-boiling hydrocarbon or equivalent material to dissolve in the oil, thereby reducing its viscosity, increasing its volume and thus Ipermitting increased recovery of the oil by subsequent water liooding. In the present invention, it is proposed to use propane or other readily liqueliable low-boiling hydrocarbon or such other liqueliable substance as possess a substantial degree of miscibility with crude oil such as liquefied carbon dioxide. The operation is carried out in manner such that only a selected section of the oil reservoir at any one time contains any substantial quantity of the added low-boiling hydrocarbon or other equivalent substance. This objective is accomplished by starting at a predetermined point at one section of an oil field and injecting therein a predetermined amount of propane or other selected material. The material is preferably introduced as a liquid but it may be injected as a gas. I-f it is actually introduced as a gas, reservoir conditions should be such that liquefaction occurs.

The amount of selected material injected should be suiiicient to establish a definite band or bank consisting essentially of the injected material in the neighborhoodof the injection well or row of injection Wells.

The liquid propane or other material is caused to flow through the field to another point or area in the field by a stream of natural gas or of inert gas such as air or combustion products injected after the introduction of the propane. By the process of the present invention, a bank of liquid propane is caused to flow through a selected path in an oil reservoir by a gas stream injected behind the propane. The flowing bank or" propane will mingle With the oil contained in the porous formation as it advances through the reservoir, so that the viscosity of the hydrocarbon mixture in the contact zone is appreciably reduced and its movement under the driving action of the gas is greatly facilitated. At the same time, the advancing bank of propane effectively dissolves out the oil which is normally retained in the interstitial spaces of the formation and replaces it with essentially pure propane. The propane being of relatively low viscosity is displaced by the driving gas much more completely than an oil of normal viscosity, and, in addition, the propane not displaced as a liquid by this means is completely vaporized and carried forward by the continued ilow of the gas which possessess a susbtantial carrying capacity for propane vapors.

After the band of propane has moved sufficiently far through the formation, it becomes relatively rich in recovered oil. It is within the scope of the present invention to remove at least a portion of the band of propane containing the dissolved oil at this point; to segregate the recovered oil from the propane and to return the propane to the formation in order to assist in maintaining a liquid bank of concentrated solvent.

Furthermore, the action of the gas drivingthe propane band on stripping and recovering residual propane from the depleted portions of the formation, will prevent the retention of appreciable amounts of propane by the already washed portions of the formation. Since the gas will tlow more rapidly through the formation than propane or oil, some propane will be carried forward from the bank by the gas stream but this propane in the gas will be absorbed from the gas by the oil ahead of the propane band. By both of these actions the maintenance of a concentrated band of propane is promoted.

It is also Within the scope of the present invention to bring the reservoir up to the desired working pressure by conventional means as by injecting natural gas before the injection of the liqueable solvent, as for example, propane. By operating in the manner proposed, the amount of propane or other selected material employed in the formation at any time may be limited to a very reasonable quantity.

The invention may be more readily understood by the drawings illustrating embodiments of the same:

FGURE 1 illustrates the invention with respect to the method of ow through an oil reservoir;

FIGURE 2 is a diagrammatic sketch illustrating the tive zones which can be anticipated when carrying out the present invention. The concentration of solvent in gas in the respective zones is illustrated by the dotted line.

Referring specifically to FIG. 1, an oil-producing formation is shown disposed below the surface of the earth 1. Well bore holes 2, 3, 4, 5 and 6 are shown extending from the surface of the earth through sub-strata 30 to near the bottom of oil-bearing formation 10. In accordance with one concept of the present invention, a predetermined amount ot' liquefied propane or an equivalent material is introduced by means of bore hole 6 into the oil-producing sand l() and is then followed by a continous injection of a suitable gas into bore hole 6. The baud of propane is shown disposed between well bore bore holes 4 and 5, flowing in the direction of bore holes 3 and 2. Oil is withdrawn from bore holes 2 and 3 together with gas which is separated from the oil at the surface and recycled to injection well 6. Since the band of propane has moved from bore hole 6 to bore hole 4, the front end of the bank contains dissolved therein substantial amounts of oil. Thus, in =accordance with one concept of the present invention, a portion of this uid may be withdrawn from the reservoir by means of borg hole 4. The oil is segregated from the propane by any1 ,i suitable means such as distillation and passed to suit-l `Lable storage. The segregated propane is preferably returned to the formation -by means of well bore hole 5 immediately back of the band of propane in the formation and ahead of the gas drive.

The gas introduced by means of well 6 serves both to drive the oil and propane bank forward and to remove the residual propane from the oil-depleted zone of the formation by vaporization.

Referring specically to FIG. 2, the condition of the reservoir is diagrammatically illustrated. After the operation of the present invention has proceeded for some time, it is anticipated that live zones exist. Zone 1 is the residual oiland propanedepleted zone in which the fluid flowing is chiefly the injected dry gas. Zone Z is one in which principally residual solvent has been left behind and wherein the solvent is being vaporized and carried forward by the gas stream. The intermediate zone (zone 3) is one in which a band of propane exists which contains in the foremost portion substantial quantities ot' recovered oil in solution. it is from this zone, and particularly from the foremost portion, that the fluid mixture may be withdrawn to the surface, the oil recovered and the propane returned to the formation, preferably into the rearmost portion of this zone. Zone 4 is one which comprises ehieliy oil being forced along ahead of the liquid propane band. This oil zone tends to dissolve out from the driving gas the propane content of the gas. The final zone is essentially unaffected by the injected solvent. The gas at this point has been practically completely stripped of its solvent and is owing toward the producing wells through a sand containing oil which has not as yet been mixed with any substantial amount of the solvent.

The present invention is broadly concerned with a novel procedure for the recovery of oil from reservoirs. In accordance with the present process, a band of relatively volatile liquid miscible with oil, as for example, C3 and C4 hydrocarbons or carbon dioxide is caused to lio-w through the formation. This band of liquid is caused to ow by utilizing a gas drive. The gas drive tends to recover from the formation the solvent used to wash out the oil. By operating as described, eicient recovery of the oil is secured through the use of a limited amount of propane or an equivalent solvent. Furthermore, eicient recovery of residual propane from the formation is readily secured.

A specific concept of the present invention is to employ the operation in conjunction with a plurality of spaced `bore holes in a particular reservoir. A solvent such as liquefied propane is introduced by means of one bore hole in a sufficient quantity followed by the introduction of gas through the same bore hole. The baud or bank of propane is caused to ow through the formation past a second spaced bore hole in the direction of a third spaced bore hole. That portion of the 4propane bank which has flowed from the first to the third bore hole contains appreciable quantities of recovered oil and can be withdrawn to the surface. The oil is separated from the propane which is preferably returned to the formation by means of the second bore hole, thus interposing the recovered and concentrated propane at a point near the rear of ythe propane bank and ahead of the gas injection point. The rearmost portion of the propane bank being relatively free of oil constituents will have a very high solvency power and will readily strip the oil formation of the remaining oil constituents. Thus, the band of propane as it flows through the formation by the operation described will have a relatively high quantity of oil in the front end of the pool and be relatively free of oil at the rear end of the moving pool, thus serving to more efficiently remove oil from the formation.

The recovery method of the present invention involves the utilization of a bank of liquid propane or other light hydrocarbons or other miscible material such as CO2 by passing these liquid substances through producing formations. The solvent can either be introduced as a gas or liquid but the conditions should be such as will result in the formation of a liquid solvent in the reservoir in the form of a bank or band. The bank is driven forward by introduction of natural gas, ue gas, inert gas, air, or combinations of `these back of the bank of solvents. The producing formation is subject to a washing action by the bank of propane or other material and, as a Conscquence, there is little oil left in the formation that has been washed. Some oil may be left due to irregularity in flow due to the fact that producing formations are not homogeneous. The gas flowing back of the bank would have residual liquid, propane, or other material vaporized into it because of the low partial pressure of these materials in the gas. Thus, the liquid propane or other rnaterials being recovered from the formation through this evaporation procedure pass along through the formation with the gas. ln accordance with the present invention, the oil is in part recovered from the formation by being increased in volume and reduced in viscosity by dilution with the solvent; but a major contribution to eompleteness of recovery results from the washing of the sand with the solvent. This washing action is basically countercurrent in nature.

As the propane travels forward` it will drive ahead of it liquid oil which can be recovered as such, with little or no propane in it up to a certain point. Back of a liquid oil layer will be a layer of a mixture of propane and oil which is preferably also produced, .that is, drawn from a well; the prop-ane may then be recovered and cycled back to the formation at a proper point. The gas used to drive the bank of solvent will move faster than the solvent itself, and as a result, it will tend .to carry propane as vapor from the propane layer into the oil layer where the propane will be absorbed. This absorption action will tend to prevent excessive Widening of the zone of oil- Ipropane mixture.

With respect .to specific operating conditions, as for example pressure, they will of necessity depend upon various eld conditions as depth of oil-producing forma tion and temperature of the reservoir. Among other fac .tors controlling operating conditions will be the solvent employed. In general, the practicable, useful control measure will be the pressure of the operation required in order to promote the maintenance of a relatively concentrated band of the solvent material. In general, the pressure should be Such as to maintain relatively pure solvent in the liquid condition, which pressure will be at least equivalent to or more generally will be in excess of the vapor pressure of the solvent at the reservoir temperature.

Generally speaking, reservoir temperatures are in the range of from 100 F. to 250 F., although lower reservoir temperatures and higher have at times been incurred. Usual reservoir temperatures are in the range from about 150 F. to 200 F. Under typical reservoir conditions, the vapor pressure of propane Will he from about to 600 pounds per square inch, and if propane is employed, pressures of this order or higher may conveniently be employed.

With respect to the rate of recycling of the gas, this quantity will in general be set at the economic optimum which reflects the pressure level, permeability of the formation, separation of the injection and producing wells, etc.

Having described the invention, it is claimed:

l. A method of recovering crude oil from a subterranean oilreservoir through a producing Well which comprises the steps of: injecting a normally gaseous solvent into said reservoir through an injection well, said solvent being characterized by a substantial degree of miscibility with oil, said solvent being liqueable at the temperature of said reservoir and being injected in suicient amount to establish a bank consisting essentially of said solvent within said reservoir in the neighborhood of said injection well; maintaining a pressure within said reservoir higher than the vapor pressure of said solvent at the temperature of said reservoir during injection of said solvent to establish a liquid bank of said solvent; thereafter injecting into said reservoir through the injection well, at a pressure suicient to maintain and drive said liquid bank toward said yproducing well, a normally gaseous drive agent which retains its gaseous state at the temperature and pressure conditions of the reservoir, said liquid solvent being capable of vaporizing into said gaseous drive agent at the pressure and temperature conditions in said reservoir; and withdrawing uids including said crude oil, said solvent and said gaseous drive agent from said producing well.

2. The process as defined in claim 1 in which said solvent is propane and said pressure maintained within said reservoir is about 200 to 600 pounds per square inch.

3. The yprocess as defined in claim l including the step of injecting natural gas into the reservoir prior to the rst injection or said solvent in order to bring said reservoir up to the pressure to be maintained within said reservoir.

4. The process as defined in claim l in which said drive agent is natural gas.

5. The process as delined in claim l in which said solvent is hydrocarbon.

6. The process as dened in claim in which said solvent ispropane and said gas drive agent is natural gas.

7. The process as defined in claim 1 in which said solvent is carbon dioxide.

8. The process as dened in claim 1 in which said reservoir is intersected by a third well positioned intermediate and spaced from said producing well and said injection Weil, said solvent is separated from said withdrawn tluids, and rsaid separated solvent is reintroduced into said bank of solvent through said third well.

9. A method of recovering crude oil from a subterranean oil reservoir through a producing well which comprises the steps of: injecting a normally gaseous solvent into said reservoir through an injection well, said solvent being characterized by a substantial degree of miscibility with oil, said solvent being liqueable and having a substantial vapor pressure at the temperature of said reservoir and being injected in sulcient amount to establish a bank Consisting essentially of said solvent within said reservoir in the neighborhood of said injection well; maintaining a pressure within said reservoir higher than the vapor pressure of said solvent at the temperature of said reservoir during injection of said solvent to establish a liquid bank of said solvent; thereafter injecting into said reservoir through .the injection well, at a pressure sufficient to maintain and drive said liquid bank toward said producing well, a normally gaseous drive agent which is normally gaseous at the temperature and pressure conditions of the reservoir, said gaseous drive agent being miscible with said solvent and substantially immiscible with said crude oil; and withdrawing said crude oil from said producing Well.

10. A method of recovering crude oil from a subterranean oil reservoir through a producing well which comprises the steps of: injecting normally gaseous hydrocarbons into said reservoir through an injection weil, said hydrocarbons being characterized by being liqueable at the temperature or` said reservoir and being injected insufficient amount to establish a bank consisting essentially of said hydrocarbons within said reservoir in the neighborhood of said injection well; maintaining a pressure Within said reservoir higher than the vapor pressure of said hydrocarbons at the temperature of said reservoir during injection of said hydrocarbons to establish a liquid bank of said hydrocarbons; thereafter injecting natural gas into said reservoir through the injection well at a pressure sufficient to maintain and drive said liquid bank toward said producing Well; and withdrawing said crude oil from said producing well.

References Cited by the Examiner UNITED STATES PATENTS 1,978,655 10/1934 Straight 16S-21 2,135,319 i1/i93s Bays 16s- 21 2,341,500 2/1944 Detling 166-21 2,347,778 5/1944 Heath i66*21 2,412,765 l2/l946 Buddrus et al 166-21 2,582,148 1/1952 Nelly 166-21 2,669,306 2/1954 Teter et al. 166-21 CHARLES E. OCONNELL, Primary Examiner.

ABRAM BLUM, BENJAMIN BENDETT, Examiners.

W. S. MCCURRY, Assistant Examiner. 

1. A METHOD OF RECOVERING CRUDE OIL FROM A SUBTERRANEAN OIL RESERVOIR THROUGH A PRODUCING WELL WHICH COMPRISES THE STEPS OF: INJECTING A NORMALLY GASEOUS SOLVENT INTO SAID RESERVOIR THROUGH AN INJECTION WELL, SAID SOLVENT BEING CHARACTERIZED BY A SUBSTANTIAL DEGREE OF MISCIBILITY WITH OIL, SAID SOLVENT BEING LIQUEFIABLE AT THE TEMPERATURE OF SAID RESERVOIR AND BEING INJECTED IN SUFFICIENT AMOUNT TO ESTABLISH A BANK CONSISTING ESSENTIALLY OF SAID SOLVENT WITHIN SAID RESERVOIR IN THE NEIGHBORHOOD OF SAID INJECTION WELL; MAINTAINING A PRESSURE WITHIN SAID RESERVOIR HIGHER THAN THE VAPOR PRESSURE OF SAID SOLVENT AT THE TEMPERATURE OF SAID RESERVOIR DURING INDJECTION OF SAID SOLVENT TO ESTABLISH A LIQUID BANK OF SAID SOLVENT; THEREAFTER INJECTING INTO SAID RESERVOIR THROUGH THE INJECTION WELL, AT A PRESSURE SUFFICIENT TO MAINTAIN AND DRIVE SAID LIQUID BANK TOWARD SAID PRODUCING WELL, A NORMALLY GASEOUS DRIVE AGENT WHICH RETAINS ITS GASEOUS STATE AT THE TEMPERATURE AND PRESSURE CONDITIONS OF THE RESERVOIR, SAID LIQUID SOLVENT BEING CAPABLE OF VAPORIZING INTO SAID GASEOUS DRIVE AGENT AT THE PRESSURE AND TEMPERATURE CONDITIONS IN SAID RESERVOIR; AND WITHDRAWING FLUIDS INCLUDING SAID CRUDE OIL, SAID SOLVENT AND SAID GASEOUS DRIVE AGENT FROM SAID PRODUCING WELL. 